Topic 8 Done Flashcards
(33 cards)
What are the sources of genetic variation?
Three sources of genetic variation are:
- mutation
- genetic recombination during sexual reproduction
- Random fertilisation
independent assortment
the random distribution of the pairs of genes on different chromosomes to the gametes. This results in many new combinations of alleles, which leads to genetic variation
crossing over
Process in which homologous chromosomes exchange portions of their chromatids during meiosis at the chiasma forming a bivalent. This leads to a change in genetic sequence (Recombinant), resulting in a new combination of alleles, and therefore genetic variation
How does random fertilisation lead to genetic variation
There are many combinations of the two gamates which ultimately fuse together to form a zygote, since ejaculation contains millions of sperm cells in which the one actually fusing with th egg cell is a random process
What is genotype and phenotype?
Genotype - Gene combination for a trait: TT, Tt or tt
Phenotype - Physical appearance of trait: Tall or short
What is gene locus
Specific site of the gene for a specific feature
What are polygenic traits? Give an example.
TRAITS CONTROLLED BY THE INTERACTION OF TWO OR MORE GENES; EXAMPLE - SKIN COLOR
What are features of oragnisms needed to carry out genetic experiments?
- Short life cycle sp that results can be seen quickly
- Produce large numbers of offpring so that the results of any crosses are statistically relevant
- Easily distinguished characteristics
- Relatively cheap and easy to take care of or manipulate to maximise chance of successful breading and minimise experimental costs
What did Mendel discover?
the basic principles of heredity by breeding garden peas in carefully planned experiments.
He crossed pure-breeding parents that had two different forms of a chosen characteristic. He discovered that some alleles are dominant over another.
Mendel’s Law of Segregation
the two copies of a gene segregate from each other during transmission from parent to offspring
Mendel’s Law of Independent Assortment
the inheritance of one character has no effect on the inheritance of another. However this law has some exceptions now with gene linkage and polygenic inheritance
What is codominance?
when both alleles contribute to the phenotype
What are recombinant phenotypes?
offspring with a phenotype different from either parent
What is gene linkage? (Autosomal)
genes located close together on a chromosome tend to be inherited together
What is sex linkage?
the presence of a gene on a sex chromosome
What is the ratio for two non-linked heterozygous phenotypes during dihybrid inheritance?
Always 9:3:3:1
Why are males more often affected by sex-linked traits than females?
Males are more often affected by sex-linked traits because they have only one X chromosome (XY), so any recessive allele on the X chromosome is expressed.
In contrast, females have two X chromosomes (XX), meaning a recessive allele can be masked by a dominant one on the other X chromosome. This makes males more susceptible to X-linked recessive disorders like hemophilia and color blindness.
What is haemophilia?
inability to clot blood (FEMALE Sex-linked disorder which involves the lack of clotting factor VIII)
What is a gene pool?
all the alleles in a population
What is the Hardy-Weinberg equation?
p^2 + 2pq + q^2 = 1
p + q = 1
p^2 = Homozygous dominant allele frequency
2pq = heterozygous allele frequency
q^2 = Homozygous recessive allele frequency
Conditions of Hardy-Weinberg Principle (5x
- No genetic drift (must be a large population)
- no gene flow (no immigration/emigration)/isolation
- no mutation
- mating must be random
- no natural selection/selection pressures
What is population bottleneck?
an event that drastically reduces the size of a population
What is the founder effect?
change in allele frequencies/loss in genetic variation as a result of the migration/isolation of a small subgroup of a population
How does population bottleneck result in disorders?
A population bottleneck reduces genetic diversity by drastically decreasing population size, leading to inbreeding. This increases the frequency of harmful recessive alleles, making genetic disorders more common/more likely to inherit.
With fewer alleles in the gene pool, there is also less chance for natural selection to eliminate these disorders
